Depends on what you mean exactly by “exposing” users. Any user that posts in the public category will be public, and then it depends on what percentage of your users will interact in that specific category.
I mean for an anonymous user to reveal the list of users. Like e.g. listing all users through API, or seeing the list in “Top Users”, or through Search function, or in any other way that I’m unaware of.
Is that because it’s considered futile to hide that data if stuff is understandably exposed in unpredictable amounts from public topic lists in any case?
I don’t think anyone planned it so much, it’s more that Discourse has two basic modes: public and private. The setting to hide the leaderboard does exactly what it says, it hides the leaderboard. Why would it do something extra?
Feel free to write up an spec of what you want, but as it’s a very boring work to do and such a niche use case you would have more luck posting it to the marketplace if you want to see it anytime soon.